Atomic layer deposition (ALD) is a deposition technique used to coat various features in the manufacturing process of circuit devices. To coat features, a film is grown layer by layer by exposing the surface to alternating pulses of reactants, each of which undergoes a self-limiting reaction, generally resulting in controlled film thickness. Each reactant exposure provides an additional atomic layer to previously deposited layers.
A film growth cycle generally consists of two pulses, each pulse being separated by purges. For oxide films, the substrate is first exposed to an oxidizing agent which results in oxygen bonding with the surface of the substrate or previous layer.
In the ideal case, the exposed surface fully reacts with the oxidizing agent, but not with itself. Next, a reactant is exposed to the surface. The reactant reacts with the previous layer to form a single atomic layer directly bonded to the underlying surface. Finally, an oxygen containing species is exposed to the substrate, which reacts with the reactant to form a finished layer.
The film growth cycle may be repeated as many times as necessary to achieve a desired film thickness. In theory, each deposited layer formed by this process is defect free. However, the practical aspects of ALD do not necessarily lead to such defect-free films in which all of the bonds are fully formed.